Terminal deoxynucleotidyl transferase-positive cells in human tonsils

To study the possible cellular origin of recently recognized indolent termi nal deoxynucleotidyl transferase (TdT)-positive T-lymphoblastic proliferati ons of the tonsils and oropharynx, we studied normal human tonsils for the presence of TdT-positive cells. TdT-positive cells were readily demonstrate d in the tonsils from 15 children and adults by immunohistochemical stainin g TdT-positive cells were distributed in discrete foci at the periphery of lobules of lymphoid tissue and adjacent to fibrous septa and had the morpho logic features of small to medium-sized lymphocytes. Double-antibody staini ng indicated the TdT-positive cells had the phenorype ofuncornmitted early I?imphoidprecursors (CD3-, CD79a-, CD10-). Foci of TdT-positive cells were not identified in 6 reactive lymph nodes studied as controls. These studies indicate that tonsils, like bone marrow and thymus, are sires of lymphopoi esis. The presence of TdT-gositive precursor cells in human tonsils may be a factor in the pathogenesis of recently described indolent T-lymphoblastic proliferations involving the tonsils and oropharynx. The presence of TdT-p ositive cells in human tonsils should not be misinterpreted as evidence of lymphoblastic lymphoma or leukemia.